UPSs and diesel generators are 2 backup systems which are kept by hosting service providers within their data centers in the event that there are interruptions in the primary power source or the current is unsound and unable to maintain the appropriate running of the web servers based in the facility. UPS refers to Uninterruptible Power Supply or Uninterruptible Power Source and it's an effective battery which works non-stop. It is connected to both the power network and the servers at all times, so when the power stops, the UPS is already operational, which prevents the servers from going down even for a second. The diesel generator is an engine which can deliver the needed electric power to keep the web servers working for a longer period of time. If there is an outage, the UPS provides the required time for the diesel generator to start and then to take over until the primary power supply is restored.